Extraction and recovery of phenols and pyridines from phenol containing oils



United States Patent 2,997,477 EXTRACTION AND RECOVERY OF PHENOLS AND PYRIDINES FROM PHENOL CONTAINING OILS Karl-Heinz Eisenlohr, Buchschlag, and Karl Grob, Frankfurt am Main, Germany, assignors to Metallgesellschaft Aktiengesellschaft, Frankfurt am Main, Germany, a German corporation No Drawing. Filed July 28, 1959, Ser. No. 829,995 Claims priority, application Germany Aug. 16, 1958 2 Claims. (Cl. 260290) This invention relates to the separation of phenols from oils containing them. Such phenol containing oils are frequently encountered in industry as, for example, in tar acid oils from coal tar, in hydrocarbon oils obtained by the hydrogenation of coal and in some of the petroleum oils. The recovery of organic nitrogen compounds (pyridines) which are present in petroleum oils and in coal tar and coal hydrogenation oils is also a part of the present invention.

At present, phenols are recovered from oils by timehonored methods involving treatment of the oil with caustic soda solutions to form aqueous solutions of sodium phenolates, from which the phenols are sprung by treatment of the phenolate solutions with carbon dioxide. The pyridines are recovered from the oils by contacting the oil with an aqueous acid such as aqueous sulfuric acid. The resulting mixture of pyridine sulfates and sulfuric acid is thereafter neutralized with aqueous alkali.

Generally the procedure followed consists in first removing the major proportion of the phenol from the oils with the aid of an aqueous solution of caustic soda leaving a residual proportion of phenol of, for example, about 4 to 5% in the oil, and therafter treating the neutral oils, containing the remaining phenols and all of the pyridine bases with an aqueous 20% sulfuric acid solution. The removal of the phenols from th pyridine-free neutral oil is thereafter completd by treating the acid oil with an aqueous solution of caustic soda. It is absolutely necessary that this procedural sequence be followed because the phenols cannot be completely removed by operating in several stages. Nor is it possible to recover all the pyridines prior to dephenolation by a single extraction with sulfuric acid, because they are contained in the oil largely bound by the phenols.

It is also known that the phenols can be dissolved out of the oils containing the same by a process which involves extracting mixtures of phenols and oils with an aqueous solution of alkali metal phenolates to form a supersaturated phenolate solution. The supersaturated phenolate solution is then treated with hydrocarbons to remove therefrom any traces of neutral oils. The removal of the remaining residual quantities of neutral oils,

especially aldehydes, has alternatively been performed by blowing out with steam.

However, it has not been possible in the past to recover both the pyridines and the phenols in the one operation. Moreover, the known methods have the disadvantage that they give rise to losses of valuable pyridines in the efliuent water waste.

According to the present invention, phenols are separated from their mixtures with oils by a process which involves extracting mixtures of phenols and oils with an aqueous solution of alkali metal phenolate to form a saturated solution of the free phenols in the aqueous alkali metal phenolates.

In order to remove the neutral oils that are taken up at the same time as are the phenols, the aqueous phenolate solution containing phenols is treated with an aromatic hydrocarbon or with a benzine fraction containing aromatics. The aqueous alkali metal phenolate solution, supersaturated with the extracted phenols,.thereby has imparted to it a content of aromatic hydrocarbon having dissolved therein traces of neutral oil. The hydrocarbon solvent and neutral oil constituents are then removed in a distilling column by blowing in steam. This procedure is usually known as open steam distillation. When they have been condensed the vapors which emerge overhead separate into two immiscible layers consisting of an aqueous phase and an oily phase. The open steam distilled aqueous phenolate solution is withdrawn from the sump ofthe column and submitted to an oxidative treatment. The phenolate solution thus obtained is then extracted in known manner with a solvent for the phenols and in particular a solvent containing oxygen, such as isopropyl ether. The alkali metal phenolate solution is then separated from the solvent for reuse and recycled to the ex traction plant for use in further extraction of phenols from the-oils or oil fractions with aqueous alkali metal phenolate solutions and thereafter extracting the phenol containing alkali metal phenolate solutions with low boiling hydrocarbons and especially aromatics, the phenols are substantialy completelytaken up in the alkali metal phenolate solution and that at the same time the valuable pyridines contained in the oil are also dissolved therein. In fact, only the unimportant high-boiling bases remain in the oil. The aqueous alkali metal phenolate solutionhydrocarbon mixture containing both the phenol and pyridine is thentreated with steam, and the hydrocarbon and any remaining neutral oils as well as the major proportion of the pyridines are driven off by the steam. The phenol-containing alkali metal phenolate solution is then extracted with isopropyl ether for the purpose of recovering the phenols. Minor traces of bases which may have remained in the phenolate solution are simultaneously dissolved in the isopropyl ether. The isopropyl ether is then first washed with dilute sulfuric acid for completely removing the nitrogen bases. After distilling off the isopropyl ether and then fractionating the phenols, phenol fractions are recovered which form clear colorless solutions and which are stable to light. These phenols are substantially free of hydrocarbons and nitrogen bases and -for this reason they are especially suitable for making :resins of the phenol-formaldehyde types.

the production of effluents contaminated by impurities It is always a disadvantage in a process if it involves which prevent such effluents from being discharged into the main drainage system. It is therefore an advantageous feature of the method according to the invention that the contaminated water from the open steam distillatio'n can be returned to the process. Hitherto, the aqueous distillate from the open steam distillation still contained about 10 to 20 g. per liter of phenols, principally cresols and xylenols. The quantity of phenols which was thus not recoverable is the equivalent of about 2 to 4% of the total pure phenols that would be available for recovery.

According to the invention these losses can be reduced by externally heating the aqueous phenolate solution that -is to be steam-distilled and by returning the condensed aqueous distillate into the process. Conveniently this may be done by adding the distillate to the aqueous phenolate solution. The addition can be made at practically any stage of the process which precedes the steam distillation. However, special advantages arise by adding the distillate to the phenolate solution before the same-ha been extracted with the hydrocarbon i.e., preferably benzine aromatic containing fraction because by diluting the phenolate solution with the aqueous phenol-containing distillate the solubility of the neutral oils in the supersaturated phenolate solution will be reduced. As a result of the dilution of the phenolate solution the activity of the phenols as solvent aids for neutral oils is diminished, so that the process of neutral oil extraction with the hydrocarbon fraction takes a more satisfactory course and requires less hydrocarbons.

If steam distillation is not performed in the preferred manner proposed by the invention i.e., by indirect heating of the phenolate solution but rather is carried out by blowing open steam directly into the phenolate solution, then the distillate cannot be recycled because the steam dilutes the phenolate solution too excessively. In such a case it is best to scrub the vapors emerging from the steam distilling column with phenolate solution or with an aqueous caustic alkali. A distillate is then obtained which still contains the pyridines but which is free from phenolate solution. In order to recover the valuable pyridines as well as the phenols in the steam distillation procedure it is advisable to scrub the vapors, whether they have arisen by direct evaporation or by the introduction of open steam, in another column or in the steam distilling column itself with an approximately 20% aqueous sulfuric acid introduced into the column from overhead. Instead or together with aqueous sulfuric acid, other dilute acids such as aqueous phosphoric acid, or hydrochloric acid may be used. The hot acid containing the pyridines can then be withdrawn at a temperature of about 100 C. from the upper part of the column and separately neutralized with aqueous alkali. Whereas in the known process of recovering the pyridines by means of aqueous sulfuric acid, neutral oils are also dissolved which must then be removed by the steam distillation of the sulfuric acid containing the pyridines, this step is unnecessary when performing the method according to the invention because at the more elevated temperature of 100 C. no neutral oils will have remained in the pyridinic sulfuric acid.

In the event that the steam distillation is performed by the direct introduction of saturated steam, the caustic soda and the sulfuric acid scrubbing processes can be combined by introducing alkali metal phenolate solution, as used in the extraction process, or on aqueous caustic soda into the column below the outlet for the pyridinic sulfuric acid for the purpose of recovering the phenols contained in the steam from the steam distillation column.

'Water is obtained overhead from the column, and contains only a slight amount of impurities, so that it can be discharged into the main drainage system.

If both caustic alkali and alkali metal phenolate solutions are used for scrubbing out the phenols, then the aqueous caustic alkali is conveniently introduced below the point of withdrawal of the pyridinic sulphuric washing acid and the regenerated phenolate solution a few trays lower down. This step has the advantage that the quantity of caustic soda required is very small.

The liquor used for washing out the phenols may again be withdrawn from the column above the admission point of the supersaturated phenolate liquor, or it may be withdrawn together with the steam-distilled supersaturated phenolate solution from the foot of the column. In the event of caustic soda being used for scrubbing the vapors evolved in the steam distillation process and this being withdrawn from the column together with the steam-distilled phenolate solution, a quantity of phenolate corresponding to the quantity of caustic soda may be branched off from the cycled phenol-ate solution, after extraction of the phenols with isopropyl ether, and decomposed with acid in conventional manner in order to recover any phenols which they may still contain.

The advantages of the procedure proposed by the invention are not confined to the fact that the phenol content of the aqueous condensate from the steam distillation process is substantially reduced, but also consist in that the phenol content of the oily condensate will be only M; to V5 of the quantity that was usually contained therein in the past.

The method according to the invention may also be modified by performing an oxidizing treatment with air or oxygen-enriched air simultaneously with the steam distillation process, irrespectively as to whether this is carried out with open steam orby applying externalheat to the supersaturated phenolate solution.

The valuable pyridines which are taken up when the oils or oil fractions: are extracted, and which appearin the aqueous and oily distillate from the steam distillation process, may alternatively 'be recovered by first condensing the vapors from the steam distillation process. The oil then separates from the Water and may be returned to the process, whereas the aqueous distillate can be conducted in known manner over an ion exchanger. The water waste which then results is practically free from pyridines, although it still contains phenols in solution. These may be recovered in conventional manner by extracting them with a solvent and returning the phenol extract thereby obtained to the oil which is to be dephenolated. However, the phenols could also be recovered with the aid of anion exchanger.

The invention will now be illustrated by the following examples:

Example 1 About 200 kg. of a 38% by weight sodium phenolate solution are introduced into the first stage of a ten-stage counter-current extractor comprising mixers and separators, and 68 kg. of an oil fraction, boiling in the range to 225 C., and having a phenol content of 20% by weight and a pyridine content of 2.5% by weight, are introduced into the sixth stage. 30* kg. of toluene enter the tenth stage of this extractor. The temperature from the first to the sixth stage is about 80 C. and from the sixth to the tenth stage between 60 and 80 C. The dephenolated oil leaves the extractor at the end where the phenolate solution enters. It contains no more than 0.3% phenols and 1.3% higher boiling pyridines, i.e. boiling above C.

The phenolate solution which leaves the extractor supersaturated with phenol and containing pyridine is steamdistilled in a column, about 20 kg. of steam being distilled 0E overhead by the application of external heat. The vapors which contain the phenols and the major proportion of the pyridines are introduced into a second column having twelve trays about half way up the column. About ,5 kg. of a 20% aqueous sulphuric acid are charged overhead into this twelve-tray column in order to scrub the pyridines from the vapors. The sulphuric acid which contains the pyridines is discharged approximately at the level of the eighth trayand since it is free from neutral oil it is directly neutralized with an aqueous alkali solution for recovering the pyridines. About 1.0 kg. of valuable pyridines are thus obtained. The vapors emerging from the column overhead are substantially free from pyridine. The condensate separates in the separator into an oily and aqueous phase. The oil is admixed with the oil that is yet to be dephenolated, whereas the aqueous distillate amounting to about 20 kg. is added to the supersaturated .the same extractor the residual pyridines are washed out of the phenol-containing ether with 0.6 kg. of an aqueous 20% sulfuric acid. Since this sulfuric acid still containsa considerable quantity of free acid it is used for scrubbing 53 out the pyridines contained in the vapors emerging from the steam still. After distilling off the ether in a distilling column and after fine fractionation, carbolic acid, cresols, and xylenols which will dissolve to form a clear solution are obtained having a pyridine content below 0.008%. The yield in refined phenols totals overall 13.3 kg. After recovery of the isopropyl ether dissolved in the phenolate liquor the latter is returned to the cycle for the further dephenolation of oil.

Example 2 100 kg. of a 40% sodium phenolate solution are introduced at one end and 17 kg. of toluene into the other end of a ten-stage counter-current extractor, 20 kg. of an oil fraction boiling between 150 and 220 C. with a 24% by weight phenol content and a 3.5% pyridine content, are introduced into the sixth stage and 3 kg. of a crude phenol boiling between 180 and 225 C. and containing 1.5% neutral oil from a water dephenolation plant are introduced into the seventh stage of the extractor.

A mixture of dephenolated oil and toluene leaves the extractor, and is separated by distillation. The toluene is recycled to the refining process, whereas the dephenolated oil is withdrawn for further processing from the foot of the column. This oil contains 0.2% by weight of phenols and 1.9% of high-boiling pyridines.

The phenolate liquor supersaturated with phenol and containing the low-boiling pyridines leaves the other end of the extractor and is steam-distilled by the application of external heat. Upon condensation, the distillate separates into two layers, an oily phase and an aqueous phase constituting about 15 kg. The oily phase containing 15% phenols is returned to the seventh stage of the abovementioned ten-stage counter-current extractor, whereas the water is taken over an ion exchanger where the pyridines are retained by an acid ion exchanger. Regeneration produces 0.4 kg. of pyridines. After having thus been freed of pyridines the water is recombined with the supersaturated phenolate liquor in the seventh stage of the above-mentioned counter-current extractor, i.e. before 4 purification with the hydrocarbons takes place. The

supersaturated phenolate solution which flows out of the steam distillation column is then processed in the same way as described in Example 1, the phenols being recovered by extraction with isopropyl ether and by scrubbing the phenol-isopropyl-ether extract with sulfuric acid. In this manner 7.7 kg. of phenols are obtained which, after having been fractionated, yield phenols which will dissolve to form a clear solution.

We claim:

1. In the process for the recovery of phenols from mixtures thereof with neutral oils in which the phenols are extracted from the mixture with an aqueous alkali metal phenolate solution, the extract washed with a hydrocarbon solvent and distilled in contact with steam, the improvement for the recovery of pyridines and additional phenol values which comprises contacting the vapors from the distillation with an aqueous acid solution, separating the pyridines from said acid solution after said contacting and thereafter recycling the phenols in the aqueous portion of the distillation product to a point in the process prior to said washing.

2. In the process for the recovery of phenols from mixtures thereof with neutral oil in which the phenols are extracted from the mixture with an aqueous alkali metal phenolate solution, the extract washed with a hydrocarbon solvent and distilled in contact with steam, the improvement for the recovery of pyridines and additional phenol values which comprises effecting said distillation by indirect heating with the internal generation of steam, contacting the distillation vapors with an aqueous acid solution, recovering pyridines from said acid solution after said contacting, condensing the distillation vapors to thereby form an aqueous and oil phase and recycling the aqueous phase containing phenols to a point in the process prior to said washing.

References Cited in the file of this patent UNITED STATES PATENTS 

1. IN THE PROCESS FOR THE RECOVERY OF PHENOLS FROM MIXTURES THEREOF WITH NEUTRAL OILS IN WHICH THE PHENOLS ARE EXTRACTED FROM THE MIXTURE WITH AN AQUEOUS ALKALI METAL PHENOLATE SOLUTION, THE EXTRACT WASHED WITH A HYDROCARBON SOLVENT AND DISTILLED IN CONTACT WITH STEAM, THE IMPROVEMENT FOR THE RECOVERY OF PYRIDINES AND ADDITIONAL PHENOL VALUES WHICH COMPRISES CONTACTING THE VAPORS FROM THE DISTILLATION WITH AN AQUEOUS SCID SOLUTION, SEPARATING THE PYRIDINES FROM SAID ACID SOLUTION AFTER SAID CONTACTING AND THEREAFTER RECYCLING THE PHENOLS IN THE AQUEOUS PORTION OF THE DISTILLATION PRODUCT TO A POINT IN THE PROCESS PRIOR TO SAID WASHING. 